I have this from a friend of mine... I haven't tried it myself, but it's interesting... see if it works for you:

Right before you leave the underdark, give all your Drow equipment to another party member, and then kick them out of the party, saying you'll meet them elsewhere later (He did this with Jahiera... I don't know if the bug is Jahiera specific or not). They'll leave, you fight your way out of the underdark, go through the foo with the elves, and then head back to the city where you meet up with said party member again... and they have all the stuff, miraculously intact.

Like I said, I haven't done it myself, but my friend swears by this work-around. Good luck!